Cosmologists Are Unable To Understand What Is Making The Galaxies Defy Cosmic Gravity Baltimore: Mario Livio tossed his car keys in the air. They rose ever more slowly, paused, shining, at the top of their arc, and then in accordance with everything our Galilean ape brains have ever learned to expect, crashed back down into his hand. That was the whole problem, explained Livio, a theorist at the Space Telescope Science Institute here on the Johns Hopkins campus. A decade ago, astronomers discovered that what is true for your car keys is not true for the galaxies. Having been impelled apart by the force of the Big Bang, the galaxies, in defiance of cosmic gravity, are picking up speed on a dash toward eternity. If they were keys, they would be shooting for the ceiling. "That is how shocking this was,' Livio said. It is still shocking. Although cosmologists have adopted a cute name, dark energy, for whatever is driving this apparently antigravitational behavior on the part of the universe, nobody claims to understand why it is happening, or its implications for the future of the universe and of the life within it, despite thousands of learned papers, scores of conferences and millions of dollars' worth of telescope time. It has led some cosmologists to the verge of abandoning their fondest dream: a theory that can account for the universe and everything about it in a single breath. "The discovery of dark energy has greatly changed how we think about the laws of nature,' said Edward Witten, a theorist at the Institute for Advanced Study in Princeton, New Jersey. This fall, Nasa and the department of energy plan to invite proposals for a $600 million satellite mission devoted to dark energy. When astronomers and physicists gathered at the Space Telescope Science Institute recently to take stock of the revolution, their despair of getting to the bottom of the dark energy mystery anytime soon, if ever, was palpable, even as they anticipate a flood of new data from the sky in coming years. When it came time for one physicist to discuss new ideas about dark energy, he showed a blank screen. The institute's director, Matt Mountain, said that dark energy had given this generation of astronomers a rare opportunity, and he admonished them to use it wisely. "We are placing a large bet,' Mountain said, "using our credibility as collateral, that we as a community know what we are doing.' But many stressed that it was going to be a long march with no clear end in sight. Lawrence Krauss of Case Western Reserve University told them, "In spite of the fact that you are liable to spend the rest of your lives measuring stuff that won't tell us what we want to know, you should keep doing it.' Through myriad techniques and observations, cosmologists have recently arrived, after decades of strife, at a robust but dark consensus regarding a cosmos in which stars and galaxies, as well as the humans who gawk at them, amount to barely more than a disputatious froth. It was born 13.7 billion years ago in the Big Bang. By weight it is 4% atoms and 22% so-called dark matter of unknown identity